You should be carrying some !Healing on-hand pretty much as soon as your max HP is large enough for it to potentially be relevant. *Healing* generally should be saved for the final fights, as should !Speed as soon as you have a Staff of Speed. ?Banish isn't that helpful in the final fights; summons will tend to have a variety of letters and/or be unique. ?MassBanish is definitely worth saving though, as is ?Destruction. I do however try to carry one ?Destruction with me for emergencies during general exploration. It's the same principle as with !Healing -- if you don't survive until Sauron/Morgoth, then there was no point in stockpiling those consumables.

The thing to be aware of with Sauron/Morgoth is that they drain charges with their melee attacks, which heals them in the process. Consequently, carrying staves or wands when meleeing them is not recommended. Staves of Speed/Destruction can be very useful in getting to the final fights, but they shouldn't be used during said fights. Though you can use them at the start and then drop them on the ground, to save yourself a potion/scroll before the fight starts.

Thanks, Derakon. It's been so long since I have encountered S and M, that I did not know about the wand/staff business.

Derakon's point about staffs and wands only holds for melee. If you're a ranger or plan to use magic and/or wands of Annihilation, take all the devices you want to the final battles. But yes, in general, save the scrolls (and potions of speed) for the end, and use staffs and wands to get yourself there.
Potions of Healing and Restore Mana are more common and can be used with discretion throughout the game. And I repeat:
Scrolls if Teleport Level are worthless against the bosses and should be your guaranteed escape of choice for the majority of the game.

I disagree with Derakon's about scrolls of Banishment: Morgoth sometimes summons Demons or Dragons, against whih these scrolls work well. And even undead summons will often have only one dangerous monster genus which can be banished explicitly, leaving some harmless monsters usefully filling up space.

Derakon's point about staffs and wands only holds for melee. If you're a ranger or plan to use magic and/or wands of Annihilation, take all the devices you want to the final battles. But yes, in general, save the scrolls (and potions of speed) for the end, and use staffs and wands to get yourself there.
Potions of Healing and Restore Mana are more common and can be used with discretion throughout the game. And I repeat:
Scrolls if Teleport Level are worthless against the bosses and should be your guaranteed escape of choice for the majority of the game.

I disagree with Derakon's about scrolls of Banishment: Morgoth sometimes summons Demons or Dragons, against whih these scrolls work well. And even undead summons will often have only one dangerous monster genus which can be banished explicitly, leaving some harmless monsters usefully filling up space.